SK66993A3 - Use of phosphonium compounds in the production of leather - Google Patents

Abstract

Hydroxyalkyl phosphine compounds, such as tetrakis (hydroxymethyl) phosphonium salts, are applied to skins or hides, or leather in finishing operations.

Description

Technical field

The invention relates to the use of hydroxyalkyl phosphine derivatives in the manufacture of skin.

BACKGROUND OF THE INVENTION

Animal skins, made up largely of proteins. are gradually decomposed by the action of microorganisms and also by autolysis. Increased mechanical. chemical and biological stability. which leather exhibits in comparison with raw hides is primarily caused by tanning, a process which, together with various finishing methods, gives the leather the characteristics that make it possible to be marketed. The tanning process is generally divided into pre-tanning, self tanning and finishing. Due to the complexity of the chemical processes used herein, the substrates that are treated under different conditions with respect to both chemical constitution and mechanical stability differ. For example, the water content of the raw skin may be as high as 80 in the treated raw skin to about 40%, and in the leather subjected to a finishing treatment it is about 10-15%. As the selection of agents for each stage is difficult, a great effort has been made to develop synthetic tanning agents to replace the commonly used chromium or vegetable tannins. However, this was mostly done on an empirical basis since the mechanism of action was not known in detail.

Attempts to explain the relevant interactions were based on various phenomena such as electrovalence, salt formation and physical absorption.

In general, crosslinking has been sought, and therefore polymerization within the substrate has been contemplated. Another requirement was to achieve hydrothermal stability with respect to shrinkage.

This is important for finished products and can thus prevent damage to the substrate during processes such as water clarification. It also improves the fixability of the substances which are applied to the surface, for example, after finishing after cleaning, if desired.

Raw hides are commonly salted or soaked in brine solution to be stored during storage prior to tanning. although sometimes raw leather is processed directly.

The skins are appropriately cleaned and scraped to remove the outer mass. They are then degreased either using a solvent preferably based on a paraffinic hydrocarbon, or preferably by heating with an aqueous degreasing solution, which is better in terms of safety and environmental impact. The aqueous degreasing solution generally comprises brine. However, heating the skins with brine causes shrinkage. The problem of shrinkage can be solved by the addition of some agents such as glutaraldehyde. This is normally added to the degreasing solution.

The main operation is tanning. In this process, the skin is contacted with various tanning agents such as vegetable tannins, mineral tanning agents such as chromium or molybdenum salts and various organic compounds, or combinations thereof.

After tanning, surface treatment agents are normally applied to the skin. A curable polymer is commonly used. It may be a natural polymer such as casein or a synthetic polymer such as polyurethane. The finishing is then cured using a cross-linking agent. Casein treatments are cured using products such as formaldehyde.

However, formaldehyde presents serious problems in the field of toxicological and environmental effects. This leads to restrictions on its use. The formaldehyde substitutes that have been used hitherto have always been considerably more expensive than formaldehyde and less effective.

SUMMARY OF THE INVENTION

It is an object of the present invention to replace formaldehyde in post-tanning operations, such as curing and finishing, particularly curing of casein coatings.

The present invention further provides a substitute for glutaraldehyde. as a shrinkage inhibitor during operations that precede tanning, such as a degreasing operation.

The present invention further provides alternatives to crosslinking agents such as aziridine, which have hitherto been used to cure synthetic polymeric skin coatings.

U.S. Pat. 3,104 151 of r. 1963 and no.

992 897 In 1959 it was proposed to use tetrakishydroxymethylphosphonium chloride together with phenols and various organic compounds of trivalent nitrogen as a tanning agent. However, this proposal has never been implemented and hydroxyalkyl phosphine derivatives have not been used in the tanning industry.

It has now been discovered that hydroxyalkylphosphines and hydroxyalkylphosphonium salts can be used as chemical crosslinking agents and can be used mainly as a substitute for glutaraldehyde in the pretreatment process and as crosslinking agents for skin treatments after tanning.

Hydroxyalkylphosphonium compounds have been used for many years in the preparation of flame retardant textiles. They are acceptable from the air protection point of view, are rapidly degradable, and have been shown to have much less toxicity compared to formaldehyde compared to higher animals and plants.

The present invention relates to the use of phosphine derivatives of the general formula I (HORPR'nOm) xXy (I) wherein R represents alkyl or alkenyl of 1 to 24 carbon atoms, R 'is the same or different alkyl or alkenyl of 1 to 24 carbon atoms or is a group -ROH, wherein R is as defined above, X is an anion which causes the compound to be at least slightly soluble in water, x is a valence of X, n is a number 2 or 3, m is a number 0 or 1, wherein (n + m) is 2 or 3 and Y is 0 or 1, wherein (n + y) is 2 or 4, or of condensates of some of these compounds, soluble at least slightly in water, for application to skins, hides or skins in pretreatment operations; or in final adjustments.

According to one preferred embodiment of the invention, the solution containing the hydroxyalkylphosphine derivative of the formula I is used for the treatment of raw hides or hides pretreated before tanning. The solution containing the hydroxylalkylphosphine derivative of the formula I is in this case added to the aqueous degreasing solution.

According to another preferred embodiment, the hydroxylic phosphine derivative of formula I is used as a curing agent in the curing of tanned leather coatings.

The phosphine compounds of formula I contain 2 or more phosphorus atoms. The compound must be soluble in water to a concentration of at least 0.5 g / liter at 25 ° C. Such phosphine derivatives contain at least one hydroxyalkyl group per phosphorus atom, preferably at least 2 hydroxyalkyl groups per phosphorus atom. These hydroxylalkyl groups generally correspond to formula II

ROH (II) wherein R is as defined above.

the ups that connect phosphorus atoms together are

-R-.

-R-O-R-R-NH-R or c - R - R '' - R where R is as defined above and R 'is a residue formed by the cleavage of two nitrogen-bonded hydrogen atoms from a di- or polyamide such as urea.

di cyanamide, thiourea or guanidine.

Such compounds with two or more.

respectively. three hydroxyalkyl groups per phosphorus atom are prepared by self-condensation of compounds having 3 or 4 hydroxyalkyl groups bonded to one phosphorus atom of formula III (HORPRnOm) y (III) wherein R, n. m and y are as defined above or with a compound of formula IV (IV) wherein R '' is as defined above.

Condensation is carried out by heating to 40-120 ° C.

The phosphine compounds preferably contain only one phosphorus atom and 3 or 4 hydroxyalkyl groups, preferably hydroxymethyl groups.

Such compounds are prepared by reaction of phosphine and aldehyde.

typically formaldehyde or ketone in the presence of a mineral acid.

most common hydrochloric acid.

sulfur or phosphorus. Depending on the ratios of the starting materials, the product may be a tris-hydroxyalkylphosphine or a tetrakishydroxyalkyl (1) phosphonium salt. The phosphonium salt tends to convert to a phosphine derivative in an aqueous alkaline medium. Simultaneously, a small amount of dimeric compound with 2 phosphorus atoms and -ROR- bridge and / or phosphine oxides is formed. Phosphorus compounds generally have a pH of 1-6 when they are in the form of an aqueous solution of a concentration by weight.

Phosphorus compounds in which one or more R is alkyl are prepared from the corresponding and alkyl-substituted phosphines by reaction with aldehydes or ketones. To avoid foam formation. it is preferred that the alkyls or alkenyls have at most 4 carbon atoms. Compounds having 1 or 2 alkyls or alkenyls containing up to 24 carbon atoms can be used in the applications of the invention. Foaming is not a problem here.

The hydroxyalkylphosphine is preferably tris (hydroxymethyl) phosphine, or a precursor thereof, more preferably tetrakis (hydroxymethyl) phosphonium sulfate.

chloride, bromide or phosphate. However, X may be any compatible anion such as nitrate.

fluoride, a phosphonate such as acetodiphosphonate, aminotris (methylenephosphonate), ethylenediaminetetrakis (methylene phosphonate) or diethylenetriaminepentakis (methylene phosphonate), condensed phosphate such as pyrophosphate.

metaphosphate, tripolyphosphate or tetrafosphate.

chlorate, chlorite nitrite, sulfite, phosphite, hypophosphite, iodide.

borate, metaborate, pyroborate, fluoroborate or carbonate or an organic anion such as formate, acetate, benzoate, citrate, tartrate, lactate, propionate.

butyrate, ethylenediaminetetraacetate, paratoluenesulfonate. a benzenesulfonate or anionic surfactant such as an alkylbenzenesulfonate, an alkyl sulfate or an alkyl ether sulfate.

The substrates to which the above compounds are applied according to the present invention are raw and tanned skins from pigs, sheep, calves, cattle, goats, reptiles, birds or fish.

They may be either crude or they may be salted or brine.

The application of the compounds can be carried out before the degreasing process with an aqueous degreasing agent and, simultaneously, by degreasing, before the tanning process.

Any tanning agent may be used for the tanning. These include vegetable tannins such as mimosa, mineral tanning agents, for example based on chromium.

% of a chromium powder consisting of 25% Cr2O3; a low chromium tanning composition of 4% chromium powder;% Cr2O3; titanium aluminum complexes; resin-based compositions such as inelamine preparations. Combined formulations are also possible. Two or more of said substances may be used simultaneously or in successive steps.

The substrates of the present invention and one preferred embodiment thereof are tanned skins. to which a finishing agent has been applied, which must then be cured. It may be casein or synthetic means such as fluorocarbons or polyurethane.

In one preferred embodiment of the present invention, raw hides, for example sheep, or especially hides, pre-treated by some process followed by tanning (e.g., soaking, liming, hair removal, pickling and finally pickling) are contacted with a degreasing solution. Typically, this degreasing solution is a brine containing from 2% sodium chloride to saturation of the solution, usually in the range of 3 to 10%, preferably 5 to 9%. According to the present invention, it will use a degreasing solution which further comprises a hydroxyalkylphosphine derivative, preferably a tetrakishydroxymethylphosphonium salt, most preferably tetrakishydroxymethylphosphonium umsulphate.

phosphonium sulphate sa

This substance. for example, tetrakishydroxyalkyl is preferably added in the form of an aqueous solution at a concentration of 0.2 to 20% by weight, typically at a concentration of 0.5 to 12% by weight, preferably further comprising additional additives.

- 9% by weight. The degreasing solution may contain substances such as detergents and wetting agents.

especially non-ionic detergents, at a concentration of 1-10% by weight.

preferably 6 wt.

When using the method according to the invention, it is advantageous to keep the pH of the degreasing solution as low as possible, preferably from 1 to 9, usually from 3.5 to 8, preferably from 4.0 to 6.5, most preferably at a value of 4.5. Too low a pH reduces the shrinkage temperature of treated degreased skins.

Most preferably, the pH of the aqueous degreasing solution is adjusted by adding the necessary amount of an alkali such as a water-soluble alkali or alkaline earth metal carbonate or bicarbonate. Such a substance is added in the form of an aqueous solution at a concentration of 1-10% by weight, preferably 1 to 2% by weight.

The hydroxyalkyl derivative of phosphorus may be added to the aqueous degreasing solution at the outset. In a more preferred embodiment, the hydroxyalkylphosphine derivative is. such as tetrakishydroxymethylphosphonium sulfate. adds, as a separate component, to a reaction system comprising the treated hides and other constituents forming the aqueous degreasing solution described above, the pH of which is adjusted to a value in the range of 4 - 8, preferably 4 - 6.5, preferably 4, 5th The process is effectively supported by constant stirring. The treatment of the skins takes place in about 1 - 32 hours at a temperature of 10 - 40 ° C, preferably 25 ° C.

Longer exposure times and elevated temperatures do not have a favorable effect and these conditions should be avoided. Too thorough degreasing is considered. as a result of reduced tear strength of the final tanned product. The skins are then generally washed with warm water at a temperature of about 50-60 ° C until the waste water is fat-free.

Another particularly preferred embodiment of the present invention is a process wherein an effective amount of a hydroxyalkylphosphine derivative, preferably an aqueous solution of tetrakishydroxymethylphosphonium salt at a concentration of about 1-10%, preferably 2-7.5%, preferably 2.5%, is applied to the tanned dry skin. to which the curable coating has been applied by a conventional method known in the art. These coatings preferably comprise pigmented or unpigmented casein or a curable resin such as polyurethane. The composition of the invention is generally applied to the skin by spraying. The skin is then dried either at room temperature overnight or alternatively at a temperature elevated for a shorter time, for example at 60 ° C for 20 minutes. These two alternatives are equivalent in terms of method success.

Alternatively, it is also possible to add the hydroxyalkylphosphine compounds of the present invention to the coating formulations while it is used for application to a particular substrate. However, their reactivity limits the use of this method, and is not suitable in conjunction with some synthetic skin finishing agents.

This indicates that it is advantageous in the practice of the invention to apply the lipid lowering compounds to the skin as a substrate by post-spraying.

The compositions of the present invention consist of a hydroxyalkylphosphine derivative. dissolved or emulsified in a liquid solvent in pressurized containers.

The compositions may further comprise other conventional components such as crosslinking agents, synergists. emulsifiers, surfactants, wetting agents and antifoams.

DETAILED DESCRIPTION OF THE INVENTION

The invention is further elucidated in the Examples which follow. In the examples, THPS stands for tetrakis (hydroxymethyl) -phosphonium sulfate. All percentages are based on the total weight of the solutions.

Example 1

Water degreasing with THPS

The customized sides of the sheepskin were trimmed in the following conventional manner:

1.0 liters of water at room temperature

450 g of lime CaCl2)

150 g of sodium sulphide is applied in an amount of 0.5 liters on one side.

Coat the reverse side of the skin.

Leave for 5 hours. The wool is removed.

Weigh again.

100% water% lime Ca (OH) 2% sodium sulfide

It rotates intermittently overnight.

100% water at room temperature% salt

Wash for 5 minutes.

% ammonium sulfate

It takes 30 minutes.

100% water

Rotate for 1 hour to reach pH 8.7.

100% water at 35 ° C

0.1% proteolytic enzyme system solution sold under the registered trademark PANCREOL IQA

Shooting for 1 hour.

Wash in cold water for 10 minutes.

100% water at room temperature% salt

Spin for 10 minutes.

% Formic acid (diluted 1 10 with water)

0.5% sulfuric acid (diluted 1 - 10 with water).

Degreasing of the peeled skins was then carried out by the process described below;

% water at 25 ° C% salt% non-ionic detergent marketed

SANDOZIN NI

It takes 30 minutes.

Add 2% sodium formate.

It takes 15 minutes.

Add 1.2% sodium bicarbonate in 3 portions, each portion every 15 minutes.

After the last addition, the pH is 4.55.

- 11 Spin another 30 minutes.

Add 1% aqueous THPS (75%).

It takes 45 minutes.

Add 1.2% sodium bicarbonate in 3 portions, each portion every 15 minutes.

pH

2. Addition 4.6

3. Addition 6.2

Drain.

Wash in water at 53 ° C.

Shoot for 30 minutes.

Repeat the wash five times until the waste water is free of fat.

For comparison, degreasing was also performed as described above, except that THPS was replaced by 3% glutaraldehyde, sold under the trademark RELUGAN GTV and using paraffin as described below.

Degreasing process using paraffin

100% paraffin at 35 ° C

Shooting for 1 hour.

Allow to drip.

100% water at 30 ° C% salt% non-ionic detergent

It takes 30 minutes.

Allow to drip.

The detergent is used 4 times.

The treated degreased samples were then tested for burst temperature and for the absence of fat.

Table 1 ^: Effect of degreasing process on burst temperature

temperature bursting and (° C) Approach Final pH whole The core reverse Paraffin 68 - THPS at 6 77 79 76 G1utaraIdehyd 6.5 82 83 82

Table 2.- Analysis of fat removal on the comparable side (double results)

Approach THPS glutaraldehyde Paraffin Skin fat after degreasing (%) 5.1 5.1 5.1 Average fat removal (5) 66 64 67

These results show that under the given conditions, fat removal using THPS is as good as using both glutaraldehyde and paraffin.

Samples from each type of treatment were then subjected to standard chromium plating and then tested by tear test. The results are summarized in Table 3.

Table 3: Tear strength of chrome tanned skins previously degreased by different procedures

Pre - processing Tear strength (kg / mm) Perpendicular to the back Parallel to the back average inspection 5.23 K) 0.51 5.85 K) 1.88 5.55 K) 1.20 G1utara1dehyd 3.89 K) 0.57 4.39 M 1.09 4.14 K) 0.82 THPS 3.93 K) 1.04 4.77 K) 1.58 4.35 K) 1.31

** degreased with paraffin

The analysis of the results shows that there is no significant difference between the different procedures. While both results (both glutaraldehyde and THPS) are weaker than the control, all types of tanning processes cause a reduction in tear strength. The results indicate that THPS has no greater effect on tear strength than glutaraldehyde. The difference in burst temperature in the standard chromium plating process is minimal and the resulting coloration is also satisfactory when compared to a paraffin-degreased control.

Example 2

Casein fixation by THPS

1. Leather type chrome-tanned sheepskin vegetable quarry tanned calf

2. Pigmentation

P ymented non-pigmented final casein treatment

3. Fixatives

0.2; 5; 10% aqueous THPS

Formaldehyde as a control

4. Drying temperature after fixation

Room temperature minutes at 60 ° C

Approach

All skin samples were sprayed with two coatings of the mixture

A. pre-drying was then carried out, two coats of mixture B were sprayed on and then dried.

Mixture i A B Earnshaw top paste (casein, 14% solids) 70 70 Earnshaw PPE white (titanium dioxide anatase pigment, 52% solid) io 0 Water 70 70

Fixation was performed in the form of a lightly sprayed coating. Drying was performed at 60 ° C for 20 minutes. Alternatively, it can be dried at room temperature. Non-pigmented samples were prepared using mixture B. All samples were kept at 20 ° C and 65% relative humidity for two days prior to glaze. They were then stored for one week under the same conditions and only then tested. Yellowing was determined. fragrance and wet abrasion strength.

The results

No sample showed signs of yellowing or noticeable odor. The number of wet abrasions on the gray scale was 3 (SLF 5). All samples without fixation loosened at 8 wet abrasions. whereas all formaldehyde- or THPS-fixed samples passed more than 1,024 wet abrasions.

In this experiment, the drying temperature does not affect the final properties of the sample.

The results show that THPS applied at 2.5% fixes casein with an efficiency equivalent to 10% formaldehyde.

Example 3

It spoils new formulations

Several selected casein products are applied to the skin. The skin was then treated with THPS or formaldehyde.

Tannin-tanned goatskin samples were treated with each of the following products (Earnshaw), the characteristics of which are further described in Table 4.

1. Chandeliers

2. Plating season

3. Top paste

4. Binder 1079

5. Glazing Binder

6. Hard Binder

7. Top finish GP

8. Top paste 7%

The finish consisted of two pigmented primer coatings and two top coatings.

Each sample was finally processed by the following

I =

1. without fixative

2. A 5% solution of 70% active THPS plus a minimum amount of anionic surfactant

3. 10% formaldehyde.

Samples were tested for wet abrasion stability before and after artificial aging in an incubator at 60 ° C for 1 month.

The results are summarized in Tables 4-6.

In all cases, THPS results were better than or equivalent to formaldehyde.

Table 4- Overview of Casein Binders

Casein bond Title Properties (5% solids spatter) 1 Luster Soft casein and wax 2 Plating Season Soft plastic casein and silicone 3 Paste Top General casein binder 4 Binder 1079 Plastic casein, soft, pleasant to the touch 5 Glazlng Binder Hard plastic casein, not recommended for use alone 6 Hard Binder Hard casein is not recommended for use alone 7 Top Finish GP Medium hard casein + shellac + wax 8 7% Paste Top General casein binder 7% solids

Table 5 = Wet abrasion stability (number of abrasions up to level 3 of the gray scale)

Casein food Title inspection 10% formaldehyde 5% (70 fab THPS% active solution 1 Luster 8 64 128 2 Plating Season 8 1 024 1 024 3 Pasta Top 8 2 048 2 048 4 Binder 1079 8 256 512 5 Glazing Binder 8 1 024 1 024 6 Hard Binder 16 512 1 024 7 Top Finish GP 16 512 2 048 8 7% Paste Top 8 2 048 2 048

Table 6- Glazing quality

Kazeí nové po j i vo Title Kontro1 a 10% formdehyde 5% THPS solution <70% active substance 1 Luster X X x xxxx 2 Plating Season x x x x xxxx xxxx 3 Pasta Top x x xxxx xxxx 4 Binder 1079 XX xxx xxxx 5 Glazing Binder XXX xxxx xxxx 6 Hard Binder xxxx xxxx xxxx 7 Top Finish GP xxx xxxx xxxx 8 7% Paste Top xxxx xxxx xxxx

Explanation of the symbols from table 6 = x without xx a little xxx could be better xxxx yes - compliant

Industrial usability

The hydroxyalkyl phosphine derivatives according to the invention are used in the processes prior to tanning as agents providing hydrothermal stability prior thereto. how water degreasing of the peeled skins is performed. They replace glutaraldehyde with no adverse effect on subsequent fat removal. Further, they are used as a post spray in crosslinking casein finishes to the skin. Here, they replace formaldehyde. There is no adverse effect on the effect and resulting characteristics such as wear and abrasion strength and adhesion.

Claims (27)

PATENT CLAIMS Use of one or more hydroxyalkylphosphine compounds of the formula I (HORPR'nOm) xXy (1) or is of the formula carbon; I v is 0 or 1, an alkenyl group having 1 to 24 different alkyl groups or a group ROH, wherein R has which causes at least moderate water, x is a valency of X. n is wherein valid. that (n + m) is 2 condensates of one or more processed skin during operations or finishing 1, characterized by alkyls or 0 or 1, wherein Cn + y) is 2 or 4, soluble wherein R represents alkyl carbons. R 'is the same alkenyl group with 1 to the above meaning, X the solubility of compounds number 2 or 3, m or 3, y is or at least mildly compounds of formula I, for applications to the raw or previous tanning process 2. Use of the compounds in which the symbols R and R 'are alkenyls having 1 to 4 carbons. of formula I as claimed in formula I represent Third Use of the compounds of the formula I according to claim 1, characterized in that the symbol y in the formula I represents 1 and the symbol 4th Use of compounds of formula 1 according to claim 1 and 3. characterized by. that R 'represents -ROH, wherein R is as defined above. 5th Use of compounds of the formula I according to claims 1 and 4, characterized in that R represents a methylene group. Use of the compounds of the formula I according to claims 1 and 5, characterized in that the hydroxyalkylphosphonous compound is a trihydroxymethylphosphine or a (hydroxymethyl) phosphonium salt. Use of compounds of formula I according to claims 1 to 6, characterized in that the symbol X in formula 1 is a sulfate, chloride or phosphate anion. Use of compounds of formula I according to claim 1, characterized in that the hydroxyalkylphosphine compound has at least 2 phosphorus atoms and at least one hydroxyalkyl group per molecule, has a water solubility of at least 0.5 g / liter at 25 ° L and is prepared by condensation of the compound of formula I alone or in the presence of urea, dicyandiamide. thiourea or guanidine. A composition for treating raw or specially treated hides prior to tanning, characterized in that it is an aqueous degreasing solution comprising a hydroxyalkylphosphine compound of formula I according to claim 1. A composition according to claim 9, characterized in that the aqueous degreasing solution is a brine containing sodium chloride in a concentration of from 2% to saturation, preferably from 3 to 10, preferably from 5 to 9%, being by weight. Mixture according to claim 9 and 10, characterized in that. wherein the hydroxyalkyl phosphonium compound is tetrakis (hydroxymethylphosphonium salt). Composition according to claims 9 and 11, characterized in that the hydroxyalkylphosphine compound is present therein as an aqueous solution with a concentration of 0.2 to 20%, preferably 0.5 to 12%, most preferably 1 to 9% by weight. A composition according to claim 9, characterized in that. wherein the aqueous degreasing solution further comprises a detergent or wetting agent. wherein the detergent or wetting agent is of a non-ionic type. A composition according to claims 9 and 13, characterized in that it contains detergent or wetting agent in an amount of 1 to 10% by weight. Composition according to claim 9, characterized in that the pH of the aqueous degreasing agent is 1 to 9, preferably 3.5 to 8, most preferably 4.0 to 6.5. Mixture according to claims 9 and 15, characterized in that the pH of the aqueous degreasing solution is adjusted by adding the necessary amount of alkaline substance before or after the addition of the hydroxyalkylphosphine compound, preferably before the addition of the hydroxyalkylphosphine compound. The composition according to claims 9 and 16, characterized in that the pH is adjusted by adding soluble alkali metal or alkaline earth metal carbonate or bicarbonate in an aqueous solution at a concentration of 1-10% by weight. 18. A method for treating raw or specially pretreated hides before tanning, characterized by. that said skins are contacted with the composition characterized in claims 9 to 17. The method according to claim 18, characterized in that. The composition is characterized in that the skin is treated with a composition characterized in claims 9 to 17 with stirring for 1 to 2 hours at a temperature of 10 to 40 ° C. A method of finishing leather, comprising applying a curable polymeric leather finishing agent and a curing agent added subsequently, characterized in. wherein the curing agent is a hydroxyalkylphosphine compound of formula I according to claim 1. Method according to claim 20, characterized in that the curable polymeric leather finishing agent is casein, optionally pigmented. Method according to claim 20, characterized in that. wherein the curable polymeric leather finishing agent is a curable resin, preferably polyurethane. The process according to any one of claims 20 to 22, wherein the hydroxylic phosphine compound is a tetrakis (hydroxymethyl) phosphonium salt. A method according to any one of claims 20 to 23, characterized in that the hydroxylic phosphine compound is applied to the tanned skin in the form of an aqueous solution having a concentration of 1 to 10%. preferably 2 to 7.5% by weight. Method according to any one of claims 20 to 24, characterized in that. The method according to claim 1, wherein the hydroxyaalkylphosphine compound is applied to the tanned skin by additional spraying. 26. A composition for finishing tanned skins by means of an additional spray, characterized by. wherein the post-spray comprises a hydroxyalkyl phosphine compound of formula I according to claim 1 and a propellant auxiliary. A composition according to claim 26, characterized in that. The composition of claim 1, wherein said composition comprises one or more crosslinking agents. synergists, emulsifiers, surfactants, wetting agents and / or antifoams.